This invention concerns a method to coil metal wire and the relative device.
The invention is applied in the field of steel production, to coil semi-worked products arriving directly from hot or cold rolling plants, such as wire, wire rods, round pieces or the like, made of steel.
The state of the art covers various methods to coil semi-worked products from the rolling plant.
According to one method, a loop-forming head is combined with a roller way system and a coil forming pit where the loops, produced by the head and made to fall progressively onto the roller system, are discharged into the coil forming pit, and superimpose themselves around a core and form the coil.
This method, although it is very commonly used, has many disadvantages in terms of the cost and bulk of the machinery, and also in terms of the stability, density and bulk of the coils themselves.
The coils formed according to this method have a low density coefficient of the loops, which is given by the ratio between the effective volume of the loops and the total bulk volume of the coil; in this case it is at most 0.15.
GB-A-924.409 teaches to prepare coils of copper wire by making a stationary container cooperate with a rotary loop-forming head which is movable axially.
The coils are deposited gradually on successive levels by force of thrust and are deposited stationary, so it is only the force of thrust generated by a drawing assembly which gives the coils the strength to maintain the position in which they are deposited.
U.S. Pat. No. 3,111,286 includes a loop-forming head which diverts the steel round piece by 90.degree. and more before delivering it to the loop-forming head proper.
The diversion by itself creates considerable problems, which are further aggravated by the fact that for many years now the rolled product has been able to travel at 100 meters per second and more.
Moreover, the diversion creates particular problems when thin rolled products are being used.
The loop-forming head cooperates with a rotary drum wherein the loops drop by their own weight as they form.
The loops, which fall due to the force of gravity, are deposited where and as they fall, without any control, and this does not ensure a satisfactory coefficient of density.
FR-A-1.425.167 includes a stationary vase or container inside which a loop-forming head cooperates; the reciprocal positions of the vase and the loop-forming head can be axially modified.
A drawing device gives the metallic wire the thrust to rest the loops under pressure on the wall of the vase or container.
Due to the force of thrust, the loop-forming head rotates, and the rotation can be adjusted with friction-generating means in order to control the resistance to rotation and therefore the thrust which can be exerted by the loops against the container.
The present applicant, who for many years now has been pressed by clients to provide a system suitable to obtain precision coils with a high coefficient of density, understood that the state of the art did not deal with the problem in the correct terms.
The applicant understood that when a loop-forming head cooperates with a stationary container, the loops formed by the head do not rotate with respect to the axis of the coil.
Consequently the loops leaving the loop-forming head tend to expand (widen) only due to the elastic reaction of deformation undergone by the rolled product as it passes from straight to circular.
The entity of this elastic force, which tends to widen the loops, depends on the characteristics of the rolled material and its physical condition; it depends for example on the temperature, which is around 700-800.degree. C.
For thin rolled products made of steel which have the normal, end-of-rolling temperature, the elastic reaction may be particularly low and insufficient to hold the loops stationary on the coil.